1. Field of the Invention
The present invention relates to a method for supplying fresh gas, preferably for use with a ventilator system for manual ventilation of a patient, in which a breathing bag is squeezed to impose an inspiration on the patient.
The invention also relates to a ventilator system operable in accordance with the method.
2. Description of the Prior Art
Ventilator systems are used for facilitating, supporting or imposing inspiration and expiration on a patient. Manual ventilation is sometimes employed when inspiration and expiration are imposed on the patient, i.e., the physician controls the patient's inspiration and expiration by means of a breathing bag. When the breathing bag is connected to the patient's airways without any intermediate pressure exchange system, the physician is able to feel the response of the lungs to the action of the breathing bag. In other words, the physician can be said to communicate directly with the lungs. This is essential, particularly in anesthesia where the anesthetist wishes to control the entire respiratory process himself/herself.
In U.S. Pat. No. 3,794,027 a manual ventilation system for anesthesia. The system includes a breathing bag which the physician squeezes to push air through a patient tube to a patient, thereby imposing inspiration on the patient. When the physician relaxes her/his pressure on the breathing bag, air from the patient can return through a carbon dioxide absorber to the breathing bag. The entire time, the physician can feel the way the patient is breathing. The bag must be periodically detached from the system, emptied and refilled with fresh gas to replace the gas re-breathed a plurality of times by the patient. In the patient tube there are also two check valves, near the patient, which respectively control the direction of gas flow to and from the patient.
Periodic evacuation of the bag has numerous disadvantages. It means that control over the patient's respiration terminates during the time it takes to replace gas, and replacement distracts the anesthetist's concentration from the patient. Moreover, gas containing anesthetic leaks into the operating theater and can have an adverse effect on surgical staff.